The attitude of a spacecraft may be controlled by various rotating inertia members, such as a reaction wheel or a control moment gyroscope (CMG). A CMG typically comprises a rotor with a fixed or variable spin rate, spinning up to 6000 rpm. The CMG may also include a gimbal assembly coupled to the rotor. The spin axis of the CMG can be tilted by moving the CMG using the gimbal assembly. This motion produces a gyroscopic torque orthogonal to the spin axis and gimbal axis.
Typically, the CMG rotor is disposed within an evacuated housing to reduce windage drag. To eliminate pressure build-up within the housing during rotor spin, at least one housing vent is provided in the CMG housing. The housing vent may be equipped with a valve that is closed when a pressure differential exists between the CMG housing and external environment and is opened when the two pressures are substantially the same.
Conventionally, a single-acting, passive vent valve has been used on CMG housing vents. The vent valve is generally coupled to the CMG housing and is in fluid communication with one of the housing vents. The vent valve is configured to vent gases between the interior and exterior of the CMG housing when the CMG is placed in a thermal vacuum chamber and the pressure is reduced during testing, or as the CMG travels out of the earth's atmosphere and reaches orbit.
Although the conventional vent valve is safe and effective, it suffers certain drawbacks. First, because the vent valve is single-acting, it typically needs to be re-seated to operate. To re-seat the vent valve, the vent valve is manually re-seated. In some configurations, the vent valve includes a valve cover that is removed. However, when the CMG is incorporated into a relatively large spacecraft the vent valve may be inaccessible, which can make manual removal of the valve cover and re-seating of the vent valve problematic. Additionally, the sealing force in the conventional vent valve may be relatively low. As a result, small leaks may develop over time, increasing the need for valve maintenance and causing reduced-efficiency CMG operation during ground testing.
Accordingly, a valve capable of passive re-seating is desirable. In addition, a valve having a higher sealing force and that requires minimal valve maintenance is also desirable. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.